As we demonstrated previously, lymphoid cells from nonsensitized syngeneic mice and decomplemented antiserum from tumor-immune mice interact to produce specific killing of tumor cells in a microcytotoxicity assay in vitro. Cytotoxicity requires the presence of both antiserum and effector cells. We propose to continue our in vitro studies of this phenomenon and to investigate the in vivo role of antiserum-dependent cellular cytotoxicity (ADCC) in the anti-tumor response. Specifically, we will: (1) further characterize the effector cells which mediate ADCC to tumor targets and the effects of immunostimulants on the effector cells. Specific immunoadsorbent columns, adherence columns and specific antisera will be used to purify K cells. Their morphology and ability to mediate ADCC to different types of target cells in 51Cr release and microcytotoxicity assays will be studied; (2) use both chemically (3-methylcholanthrene) and viral (Moloney sarcoma virus) induced tumors in experiments to determine what role ADCC plays in vivo. Specific antibody plus K cells or other effector cells will be used in attempts to influence the course of tumor growth and to prevent metastasis; (3) assess the effects on lymphoid cell populations of the non-Ig early-appearing arming factor which we previously described and which induces specific cell mediated cytotoxicity to tumor cells.